The subject invention relates to a powder atomizer as well as to a method for the series coating of workpieces with powdered coating material according to the preamble of the independent claims. In particular, the invention relates to an electrostatic rotation atomizer with a powder atomization bell which, during operation, is under a high-voltage potential, and which is like the ones used for the series coating of car bodies.
In such rotation atomizers, it is known (Dürr/Behr type N34040001) that the powder-air mixture is supplied through external hoses and led within the atomizer through the hollow shaft of the drive turbine in a slit-shaped channel in the inside of the bell plate attached to the hollow shaft. The powder flows in this slit channel as a result of the forces of rotation toward the external edge of the bell plate, where it is atomized as it exits into the open. The slit channel is connected within the hollow space formed by the hollow shaft and the bell driving collar connected to it, with the opening of the powder channel running through the hollow shaft.
In powder atomizers, the problem consists of the fact that the coating material can be deposited not only in the supply lines and in the powder channel inside the atomizer, but also in the path of the powder-air mixture after its exit from the opening of the powder channel into a rotation atomizer, and particularly in the slit channel of the bell plate. The phenomenon is also known as impact fusion. For the elimination of these powder deposits, for example, in case the operation required a color change, rinsing air is introduced into the atomizer through an external powder hose. Furthermore, the deposits in the bell plate are manually removed after the disassembly of the bell plate parts in contact with the slit channel. The disassembly and the manual cleaning of the bell plate are labor-intensive and time-consuming procedures, and they do not eliminate the risk of a narrowing of the cross section or even a clogging in the bell plate during the operation. The cleaning of the atomizer with the air supplied through the external powder hose, in contrast, can turn out to be unreliable and unsatisfactory for various other reasons. On the one hand, a considerable consumption of energy is required to convey the rinsing air through the external powder hose because of the latter's length, if a cleaning effect is to be achieved. Furthermore, the air provided for the cleaning is, at least at the beginning, itself contaminated with such an amount of residual powder from the hose that a cleaning effect occurs only after a relatively long time, which is then lost for the coating operation. During the coating operation, other instabilities can occur besides the risk of clogging. Because, in known rotation atomizers, the proportion of air in the powder-air mixture is determined only by the metering system (for example, injector or powder pump), pump effects and undesired changes in the powder-spray jet can occur, especially in conveyance systems which use little air.
The problem of the invention is to provide powder atomizer or powder coating methods which prevent disturbances of the operation, in particular due to powder deposits, in a simple, reliable and time-saving manner.
This problem is solved by the characteristics of the claims.